Liquid crystalline polyesters are good in heat resistance, flowability, dimensional stability, flame retardancy and the like, and therefore are used in electric and electronic fields. In recent years, the demand for liquid crystalline polyesters has expanded, and especially the demand for highly heat-resistant liquid crystalline polyesters showing a thermal deformation temperature of 300° C. higher, called type I, is expanding. As liquid crystalline polyesters, known are liquid crystalline polyesters having the structural units obtained from p-hydroxybenzoic acid or 2-hydroxy-6-naphthoic acid as mesogen units, liquid crystalline polyesters having an aromatic diol/an aromatic dicarboxylic acid copolymerized with the structural units obtained from 2-hydroxybenzoic acid or 2-hydroxy-6-naphthoic acid, liquid crystalline polyesters having a polyalkylene terephthalate copolymerized with the structural units. Among them, it is known that a liquid crystalline polyester with 2-hydroxy-6-naphthoic acid as mesogen units is more excellent in dielectric property, dimensional stability and light resistance, though worse in heat resistance, than a liquid crystalline polyester with p-hydroxybenzoic acid as mesogen units (for example, JP 56-10562 A, JP 2002-37869 A, JP 2004-196930 A, JP 2004-244452 A, JP 2005-213418 A and JP 2007-100078 A).
JP 56-10562 A describes a liquid crystalline polyester obtained by copolymerizing 2-hydroxy-6-naphtoic acid, an aromatic diol and an aromatic dicarboxylic acid. However, a liquid crystalline polyester composition obtained by copolymerizing 2-hydroxy-6-naphthoic acid, an aromatic diol and an aromatic dicarboxylic acid has a low melting point and is not sufficient in heat resistance. JP 2002-37869 A describes a liquid crystalline polyester obtained by adding additives to a specific monomer. However, owing to the influence of the additives, heat resistance and dielectric breakdown resistance decline. Each of JP 2004-196930 A, JP 2004-244452 A, JP 2005-213418 A and JP 2007-100078 A describes a liquid crystalline polyester obtained by copolymerizing 2-hydroxy-6-naphthoic acid, an aromatic diol and an aromatic dicarboxylic acid. However, in JP 2004-196930 A, JP 2004-244452 A, JP 2005-213418 A and JP 2007-100078 A, since solid-phase polymerization is performed for enhancing the molecular weight, the polymer is low in randomness and is insufficient in dimensional stability and flowability.
It could therefore be helpful to provide a liquid crystalline polyester having specifically excellent flowability, low anisotropy, toughness, low self-gasification capability, excellent heat resistance and high dielectric breakdown resistance, a production process therefor, a composition thereof, and a molded article composed thereof.